Recurring Meeting of Cleveland Clinic - University of Utah

Date: November 25, 2013

Time: 11:00 AM EST

Means: Conference call

Attendees:

1. Ahmet Erdemir (Cleveland Clinic)
2. Jason Halloran (Cleveland Clinic)
3. Snehal Chokhandre (Cleveland Clinic)
4. Jeff Weiss (University of Utah)
5. Steve Maas (University of Utah)
6. Ben Ellis (University of Utah)

Agenda:

1. Discuss assigned task progress.
2. Discuss FEBio feature request and test problems.

   • http://wiki.simtk.org/openknee/Specifications/FebioFeatures

3. Decide tasks for next meeting.
4. Other

Immediate action items:

Notes:

1 and 2. Discuss assigned task progress and FEBio feature request.

• In-situ strain
  • Ahmet had assigned two tasks to the Utah team: 1. Implement in situ strain feature in FEBio and, 2. document the progress in Wiki.
  • Steve implemented the algorithm which allows to prescribe a fiber stretch (transversely isotropic material) and strain is generated entirely by the fiber stretch. User specifies the fiber stretch, the algorithm makes sure the stresses are equilibrated while applying the stretch.
  • To illustrate that an example was also provided a showing constant in-situ fiber stretch of 50% enforced on a cubical block. A similar implementation was also done to replicate an open angle experiment done on arteries (3% fiber stretch, fibers oriented along the circumference, outer ring in tension, inner ring in compression, radial cut relieves the stresses).
  • This is a multi-step analysis (tied interface is active, stretch is applied, in the second step tied interface is removed). The goal here is to explore both quasi-static and dynamic analysis.
  • A solution that works regardless of the analysis (dynamic vs quasi-static), would be ideal.
  • This algorithm enforces the desired fiber stretch by adjusting the overall deformation gradient using an iterative process (Lagrangian framework).
  • In terms of pre-tensioning ligaments in the Open Knee model, the current feature should work and the next step would be to take femur-ligament-tibia from the model to confirm the implementation of the algorithm/ feature.
  • The test problem (provided by Jason) needs to be implemented before an actual Open knee model application.
  • This framework works when the reference configuration is not known but the in-situ strain is known. A framework needs to be developed to accommodate cases where reference configuration is known, a pre-tension value is desired etc.
  • This feature applies to transversely isotropic Mooney-Rivlin materials, the implementation in a general 3D framework needs to be evaluated.
• Rigid-body kinematics representation
  • Need to be able to prescribe kinetics at the joint based on a clinical coordinate frame
  • Details about the coordinate frames was added.
  • The figure was created by Ahmet to illustrate the coordinate frames. This illustrates embedded axes in each of the bones (femur and tibia). In the femur frame

3. Decide tasks for next meeting

4. Other

• None noted.